1. Field of the Invention
The present invention relates to a fast comparator circuit.
2. Related Art
A comparator is a circuit that compares two input voltages and makes a decision as to which of the two inputs is greater. FIG. 1 illustrates a simplified block diagram of a standard fast comparator 100. Fast comparator 100 includes an input amplifier 102 and a latch 104. Fast comparator 100 compares an input voltage V.sub.IN to a reference voltage V.sub.REF and produces complimentary outputs Q and Q where: when Q=1, Q=0, then V.sub.REF &lt;V.sub.IN, and when Q=0, Q=1, then V.sub.REF &gt;V.sub.IN.
It is convenient to think of a comparator as an ideal switching circuit for which any small differential input voltage, however small, results in a sudden change at the output. In reality, the switching performance of a comparator 100 depends on the gain properties of the amplifier 102. Smaller input signals tend to cause a greater propagation delay and a slower rise or fall time at the output of comparator 100. So the amplifier is a very important element of the fast comparator 100.
Once the amplifier 102 completes amplification, an amplified differential voltage V.sub.REF -V.sub.IN can be latched by the latch 104. The amplifier 102 must provide sufficient amplification of the differential voltage or the latch 102 will make a wrong decision due to noise at the input of the latch.
On an IC chip, comparators 100 are widely used for many different applications. For example, comparators 100 are used in flash converters with one flash converter typically having 100 or more comparators.
Therefore, there is a need to reduce the size of conventional comparators so that they occupy less area (e.g., real estate) on a chip. There is also a need to reduce the number of transistors a comparator 100 employs to reduce their power consumption and increase their speed.